Project Summary During animal development and adulthood, cells undergoing apoptosis, a cell death process essential for animal development and homeostasis, are rapidly internalized by other cells via phagocytosis (engulfment) and degraded inside engulfing cells. The removal of apoptotic cells provides a safe means for eliminating unwanted and dangerous cells from the body. Furthermore, it prevents tissue injury, inflammatory responses, and auto-immune responses that could be induced by the content of dead cells. The study of apoptotic-cell removal has also inspired the development of novel cancer treatment strategies. My long-term objective is to understand the molecular mechanism that controls the recognition, engulfment, and degradation of apoptotic cells, using the nematode Caenorhabditis elegans as a model organism. We believe that what is learnt from C. elegans will be translated to humans. This project studies mechanisms that drive the degradation of apoptotic cells, which are internalized into host cells, confined in a vacuolar structure called ?phagosome?. Phagosomes undergo a ?maturation? process through a series of membrane trafficking events and the end result is the degradation of cargos in the lumen. Our studies will reveal the temporal regulation mechanisms of the production (Aim 1) and turnover (Aim 2) of phosphatidylinositol 3-phosphate (PI3P), a lipid second messenger that plays an essential role in initiating phagosome maturation, on phagosomes, and how PI3P triggers the maturation process (Aims 3). Our study of the PI3P signaling mechanisms will shed light not only on the degradation of apoptotic cells, but also broadly, on the molecular mechanisms behind other PI3P-mediated membrane trafficking events, including endocytic trafficking and autophagy.